It is known in the prior art that aromatic ketones such as acetophenone, benzophenone, benzoin ethers or chlorothioxanthones are used as photosensitizers for the polymerization of polymerizable monomers such as vinyl monomers. For example, U.S. Pat. No. 3,374,160 discloses the use of ortho-bromoacetophenone as a photosensitizer. Other prior art references use some special classes of acetophenones which possess ether groups which are either alpha to the carbonyl group, or possess halomethyl groups which are alpha to the carbonyl group or which possess halmethyl groups attached to the aromatic ring. However, acetophenones which possess ether groups alpha to the carbonyl group are relatively difficult to prepare and thus, will be relatively expensive to use. Likewise, acetophenones which possess a halomethyl group alpha to the carbonyl group or which possess a halomethyl group attached to the aromatic ring are unstable and, in addition, possess lacrimogynic properties which severely limited use of these compounds.
While the above compounds are used as photosensitizers, it is also necessary to utilize activating compounds in combination with the acetophenones. These initiating compounds usually comprise an amine such as dimethyl ethanol amine, diethyl ethhanol amine, etc.
In contradistinction to this, it has now been discovered that by utilizing a certain class of substituted acetophenones and particularly alpha-aminoacetophenones of a type hereinafter set forth in greater detail, it is possible to effect the photopolymerization of polymerizable monomers in the presence of only one type of compound, said compound acting as both an initiator and a sensitizer.